1. Field of the Invention:
The present invention relates to a steering control apparatus for a motor vehicle having steerable front and rear road wheels, and more particularly to a steering control apparatus for a motor vehicle in which rear road wheels can be turned by an electric motor energized by a vehicle-mounted battery in response to the steering action of front road wheels.
2. Description of the Relevant Art:
There are known motor vehicles in which both front and rear road wheels are steerable. In some of such motor vehicles, the direction and angle of turning movement of the rear road wheels with respect to the front road wheels are controlled dependent on the speed of travel of the motor vehicle for improved steering performance. Japanese Laid-Open Patent Publication No. 63-103763 (corresponding to U.S. Ser. No. 109,232) discloses a steering apparatus for a motor vehicle with steerable front and rear road wheels, the steering apparatus including a rear wheel steering mechanism actuatable by an electric motor for turning the rear road wheels.
In the disclosed steering apparatus, the power output from the electric motor is transmitted through a ball-and-screw mechanism to the rear wheel steering mechanism. Since the electric motor is energized by a vehicle-mounted battery, the electric power supplied to the electric motor tends to vary due to a fluctuation in the voltage of the battery. Therefore, the speed at which the rear road wheels are turned is varied as the battery voltage fluctuates, giving the driver of the motor vehicle a bad steering feeling.